Without breath, life ceases. Oxygen—the second most abundant element in air—is essential for the numerous metabolic processes that sustain human life. While humans can survive without food for weeks and without water for days, survival is counted in minutes if the supply of oxygen ceases. And even if restored, brain damage may result if the oxygen deprivation was too long; the severity increases with each passing minute.
Generally, sources of oxygen for treating acute medical conditions are not readily available for members of the public to help a victim before first responders arrive, and the attendant delay in administering oxygen before such trained help arrives may result in further injury or death. First responders typically arrive with an oxygen source, usually a compressed gas cylinder. Those oxygen cylinders are heavy, cumbersome, costly to transport, and potentially dangerous. For example, the Department of Veterans Affairs warns that an oxygen cylinder can be turned “into a missile” if a cylinder fractures, and the “[e]scaping gas will propel the cylinder with enough force to penetrate cinder block walls.” See http://www.patientsafety.va.gov/professionals/hazards/oxygen.asp. Use of gas cylinders requires training to ensure safe and proper administration of gas to a patient—members of the public, for the most part, lack such knowledge.
Other devices for delivering oxygen include oxygen concentrator machines. These devices use electrically-powered mechanisms to separate oxygen from ambient air and deliver an oxygen-rich stream of gas to a patient. Shortcomings for these devices include the fact that they are often quite heavy, require batteries or some other power source, and are noisy. Thus, their use in emergent situations is limited to places where power is available, either to operate the device itself or to keep on-board batteries sufficiently charged. Additionally, as oxygen concentrators depend on the quality of the ambient air, their use is negatively affected in heavily polluted areas. Also, altitude affects the delivery of oxygen from these types of devices.
Another solution to the delivery of oxygen in emergent situations is a chemical oxygen generator, which is a device that releases oxygen via a chemical reaction. One example, sometimes called an “oxygen candle,” relies on the combustion of a chemical reaction to release oxygen. The oxygen source is an inorganic superoxide, chlorate, or perchlorate mixed with a combustion agent, such as iron. A firing pin ignites the mixture. And while such devices can deliver oxygen in an emergency, they operate at an extremely high temperature and are potentially a fire hazard. To protect surrounding structures, significant thermal insulation must be provided.
Combustion-driven generators have been around for some time and are still used, for example, in the airline and mining industries. In commercial aircraft, this type of emergency oxygen is available to passengers to protect them from cabin pressure drops (the cockpit crew uses compressed oxygen canisters instead). Modern aircraft systems generally use the decomposition of a mixture of chlorates, perchlorates, and sometimes superoxides that decompose exothermically above 400° C. to produce oxygen and salt. Ignition using an explosive cap causes the dry chemicals to react, resulting in oxygen production. While such systems can reliably produce oxygen for periods of 15 minutes or longer, the storage of explosive and flammable materials on board a commercial aircraft poses significant safety risks. And while the chemical mixtures in these devices can be stored almost indefinitely at both cold and hot temperatures, there have been real world tragedies. For example, on May 11, 1996, accidental ignition of generators in the aircraft's cargo hold caused the ValuJet Flight 592 crash. Ten years earlier, on Aug. 10, 1986, an ATA DC-10 was destroyed while parked at O'Hare Airport due to the accidental activation of an oxygen generator. And on Feb. 24, 1997, a fire broke out on the Russian Mir space station after a cosmonaut ignited an oxygen-producing perchlorate canister to supplement the space station's air supply.